Seawater isotopic (δ¹⁸O, δ²H) observations from expedition ARTofMELT, Arctic Ocean, 2023

Ben Kopec, Valtteri Hyöky, Eric Klein, Jeffrey Welker

The dataset presented here contains 5-minute resolution processed seawater isotopic measurements (δ¹⁸O, δD, deuterium excess) measurements made during the expedition ARTofMELT 2023 with Swedish icebreaker Oden in the Fram Strait pack ice during the spring transition, 10 May to 14 June, 2023.

The seawater was sampled from the underway seawater intake system (~8 m depth).

These water isotopic observations trace ice-ocean-atmosphere interactions across a range of sea ice conditions, including identifying ocean freshwater content and sources (e.g., sea ice meltwater).

Map

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Leaflet | Map data from Gebco

Citation

Ben Kopec, Valtteri Hyöky, Eric Klein, Jeffrey Welker (2025) Seawater isotopic (δ¹⁸O, δ²H) observations from expedition ARTofMELT, Arctic Ocean, 2023. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/oden-artofmelt-2023-seawater-isotopes-1

References

Kopec B, Klein E, Welker J (2022) Continuous seawater isotopic (δ¹⁸O, δD, and d-excess) observations from 2021 Arctic cruise on United States Coast Guard Cutter Healy. Arctic Data Center. https://doi.org/10.18739/A2862BC9W

Kopec BG, Klein ES, Feldman GC, Pedron SA, Bailey H, Causey D, Hubbard A, Marttila H, Welker JM (2024) Arctic Freshwater Sources and Ocean Mixing Relationships Revealed With Seawater Isotopic Tracing. Journal of Geophysical Research: Oceans 129. https://doi.org/10.1029/2023jc020583

Kopec BG, Hyöky V, Klein E, Welker J (2025) Water vapor isotopic (δ¹⁸O, δ²H) observations from expedition ARTofMELT, Arctic Ocean, 2023. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/oden-artofmelt-2023-water-vapor-isotopes-1

Data description

The data is provided in one comma-separated values (csv) file with the following columns:

• datetime date and time
• d18O_seawater −δ¹⁸O (‰)
• dD_seawater δD (‰)
• dex_seawater deuterium excess (‰)

The temporal resolution is 5 minutes. Missing data are represented by empty cells.

Comments

Measurement system

The seawater analyzed in this dataset was sampled through icebreaker Oden’s underway system that continuously cycles seawater from approximately 8 m below the ocean surface. A Picarro L2140-i analyzer (contributed from Eric Klein’s lab at University of Alaska Anchorage) combined with a Picarro Continuous Water Sampler (CWS) continuously measured that seawater for its oxygen and hydrogen isotope ratios (δ¹⁸O and δD, respectively) at ~1 Hz resolution. Deuterium excess (d-excess; d) values computed in the form of d=δD-8·δ¹⁸O. After calibration (described below), all data is aggregated to 5-minute averages. Any missing data is due to either during times of standard water calibrations or during times of instrument failures or not in operation.

Calibration

A detailed calibration protocol for these seawater isotopic analyses is described Kopec et al. (2024), with additional cruise specific information included below.

Significant offset exists between the raw measurement values and the actual values of the water sample in this system, so calibration is critical. Calibration of this seawater isotope data was performed in two steps:

1. Standard water correction.
2. Discrete underway sample correction. First, two known standard waters were measured approximately every 12 hours over the duration of the cruise. The two standards include Fiji water (δ¹⁸O = -6.56‰, δD = -42.2‰) and Anchorage Tap Water (δ¹⁸O = -19.23‰, δD = -146.61‰), and are used to place the data on the Vienna Standard Mean Ocean Water-Standard Light Antarctic Precipitation (VSMOW-SLAP) scale. A spline fit (λ=0.001) is applied to all standard water measurements, and used to calculate the offset between the raw measurement and the actual value.

The second calibration step is performed to account any additional offset created by the CWS. Discrete water samples were collected from the underway system and analyzed on a separate Picarro L2130-i analyzer in Jeffrey Welker’s lab at the University of Oulu. These discrete measurements were compared to the continuous measurements taken from the same water at the same time. A correction curve was computed from the difference between these discrete and continuous samples, and applied to the continuous measurements to correct for this effect. No water concentration effect was observed from this cruise, unlike the US Coast Guard Cutter Healy 2021 cruise presented in Kopec et al. (2024). Nevertheless, a similar discrete sample correction is still taken to follow the same approach and produce comparable data to that study.

Associated datasets

This dataset is directly complementary to the continuous water vapor isotopic observations during ARTofMELT produced by Kopec et al. (2025).

The dataset is also complementary to other seawater isotopic datasets measured following this approach (e.g., Kopec et al. 2022).

The expedition

Data were collected during the ARTofMELT 2023 expedition on board the Swedish icebreaker Oden, which was organized by the Swedish Polar Research Secretariat from 8 May through 14 June, 2023.

Data creators' roles